Bloated Mail within settings

My wife has a 16gb iPhone 6 running the latest iOS (10.0.2)
She was getting the dreaded "not enough space" pop-ups. so she deleted some pictures, then went and looked around and she noticed her Mail had 1.4gb space used under Storage &iCloud usage.

she tried to delete all emails within Inbox, Sent, Trash, Drafts. and even removed both email accounts (she has an iCloud and a GoDaddy-based work email). She had ZERO mail and no accounts. we restarted her devices and it was still showing 1.4gb of space. at times it has dipped to 1.2 or gone up to 1.44 or a little higher.

I have exhausted my minimal knowledge of trying to solve this. Anyone have any ideas?
I suppose a wipe and restore could help but that seems like a last resort and we are trying to figure out Why this is even a problem/issue.

PS. she is now hearing a BUZZ from fetch email but no on-screen display of the email (when in lock mode) I tested mine and I can get an email to pop-up on the lock screen when I get one.

Thanks in advance for any help. maybe an updated iOS 10 could help one day

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